From: Liu Yu <allanyu...@tencent.com>
3.12-stable review patch. If anyone has any objections, please let me know.
===============
[ Upstream commit 0cda345d1b2201dd15591b163e3c92bad5191745 ]
commit b9f47a3aaeab (tcp_cubic: limit delayed_ack ratio to prevent
divide error) try to prevent divide error, but there is still a little
chance that delayed_ack can reach zero. In case the param cnt get
negative value, then ratio+cnt would overflow and may happen to be zero.
As a result, min(ratio, ACK_RATIO_LIMIT) will calculate to be zero.
In some old kernels, such as 2.6.32, there is a bug that would
pass negative param, which then ultimately leads to this divide error.
commit 5b35e1e6e9c (tcp: fix tcp_trim_head() to adjust segment count
with skb MSS) fixed the negative param issue. However,
it's safe that we fix the range of delayed_ack as well,
to make sure we do not hit a divide by zero.
CC: Stephen Hemminger <shemmin...@vyatta.com>
Signed-off-by: Liu Yu <allanyu...@tencent.com>
Signed-off-by: Eric Dumazet <eduma...@google.com>
Acked-by: Neal Cardwell <ncardw...@google.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Jiri Slaby <jsl...@suse.cz>
---
net/ipv4/tcp_cubic.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c
index b6ae92a51f58..894b7cea5d7b 100644
--- a/net/ipv4/tcp_cubic.c
+++ b/net/ipv4/tcp_cubic.c
@@ -408,7 +408,7 @@ static void bictcp_acked(struct sock *sk, u32 cnt, s32
rtt_us)
ratio -= ca->delayed_ack >> ACK_RATIO_SHIFT;
ratio += cnt;
- ca->delayed_ack = min(ratio, ACK_RATIO_LIMIT);
+ ca->delayed_ack = clamp(ratio, 1U, ACK_RATIO_LIMIT);
}
/* Some calls are for duplicates without timetamps */
--
1.9.3
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